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'[OT] Muscle contraction. was: cats! -Reply'
1999\09\13@071720 by Caisson

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> Van: Kevin Allenzovic <spam_OUTMETakeThisOuTspamDOH.HEALTH.NSW.GOV.AU>
> Aan: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Onderwerp: Re: cats! -Reply
> Datum: vrijdag 10 september 1999 7:02
>
> This sounds a little impossible as AC would alternately contract and
release your muscles forcing you to release it! This is one of the reasons
we have AC supplied to our home and not DC, among ather obvious reasons.
> Edison pushed for the use of AC by demonstrating on a horse. He'd fist
hit it with AC and watch it bolt. When caught he'd again shcok it with DC
killing it stone dead.

No, you won't.  Muscles are *NOT* current-direction sensitive !  AC (in a
50 or 60 Hz cycle) only means that your muscles are not contracted the
whole time. just about 100-120 times a second.  In the time between *you*
would have to force your hand open & retreat.  I wish you good luck with
that.

By the way:  Your example with the horse does not prove that you will be
"repelled" by a AC current, just that AC is not as deadly as DC.  And
that's because your (or the horses) hart will try to beat in a 100-120 Hz
rithm.  And that goes better than trying to beat when a DC current
constantly pull's the hart-muscle together ...

My 0.02 cents.

Greetz,
 Rudy Wieser

1999\09\13@173557 by Russell McMahon

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All this out of my head - probably approximately correct but don't trust
your life to it:

Defibrillation (or more properly here, fibrillation) depends not only on
current but also on duration. RCDs are designed to disconnect power within a
critical period. I think it's within 50mS (which fortunately makes sense in
the context of 50Hz (or higher) mains frequencies) and corresponds to a
critical period during the heart's cycle. In fibrillation the normal voltage
patterns of the heart are disturbed and while it may still oscillate it may
subsequently do so in a  mode which is not conducive to pumping blood. The
television (and real life) "300, joules, clear, zap" routine is designed to
polarise the muscle, clear all oscillation patterns and let the oscillator
try and start clean again. (Master Reset).

As you'll well appreciate if you've "field tested" one, an RCD does not stop
you receiving a shock (the kick is not necessarily pleasant) but strictly
limits the duration.



RM



From: G.C. <gary.cadmanspamKILLspamTIUK.TI.COM>

>I think that these figures air on the side of caution. An RCD usually has a
trip of 30mA all though you can get them in many sizes.
>When I last looked at these type of figures I recall a statement that 30mA
at 40V was sufficient to cause defiblaration.
>
>Jim Main wrote:
>>
>> I found the following pertinent info in a mag the other day, detailing
>> whether or not you'd be able to let go a live source - it depends on the
>> amount of current that's flowing through the muscle.. and gave the
following
{Quote hidden}

1999\09\13@174222 by Sean H. Breheny

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Once again I must plead ignorance: Could someone please tell me what an RCD
is?

Thanks,

Sean

At 07:48 AM 9/14/99 +1200, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
EraseMEshb7spam_OUTspamTakeThisOuTcornell.edu ICQ #: 3329174

1999\09\13@194613 by Richard Prosser

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Residual current device (detector?)

Basically an mcb type device that opens if the difference between phase &
neutral current exceeds a specified amount (5, 10 & 30mA are typical). The
difference current is assumed to be finding an alternative path via earth
and could then represent a hazard.

Richard

> {Original Message removed}

1999\09\13@200237 by Sean H. Breheny

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Hi Richard,

Thanks. Isn't this the same thing as a GFCI? I guess I have just never
heard it called an RCD. I have never heard the term "MCB-type device"
either. I assume "CB" stands for circuit breaker?

Thanks,

Sean

At 11:43 AM 9/14/99 +1200, you wrote:
>Residual current device (detector?)
>
>Basically an mcb type device that opens if the difference between phase &
>neutral current exceeds a specified amount (5, 10 & 30mA are typical). The
>difference current is assumed to be finding an alternative path via earth
>and could then represent a hazard.
>
>Richard

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
shb7spamspam_OUTcornell.edu ICQ #: 3329174

1999\09\13@203153 by Richard Prosser

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Yes - sorry - we get so used to our local jargon
MCG = miniature circuit breaker - as opposed to MCCB - moulded case circuit
breaker
I've also seen RCDs called "Earth Leakage Circuit Breakers" - elcbs

Haven't come across GFCI but could well be the same thing

Richard

> {Original Message removed}

1999\09\13@203519 by Sean H. Breheny

face picon face
Ok, it all makes sense now, thanks.

GFCI = Ground Fault Circuit Interrupter

Sean


At 12:28 PM 9/14/99 +1200, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
@spam@shb7KILLspamspamcornell.edu ICQ #: 3329174

1999\09\13@204356 by Richard Prosser

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Thanks
A minor correction:-
MCG in my previous should of course be MCB.

I think that strictly speaking actually a ELCB incorporates both MCB and RCD
functions
Richard

> {Original Message removed}

1999\09\13@205809 by Russell McMahon

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RCD = Residual Current Device.

Measures difference between current in phase and neutral leads.
Turns off power QUICKLY when the difference exceeds some pre-set value.
A simple way to do this is to wind a few turns on a toroid from each leg so
that the net currents sum to zero when they are balanced.

When you get a return path to ground the go and return currents differ and
the system shuts down. Speaking from experience (I think I was trying one
out to see what it felt like :-)) you get a short sharp kick and then the
power is gone.

I don't recommend anyone tempting fate like this.
If I MUST test something for liveness using my body (and the situations are
few and far between) I make a closed fist and use the back of my hand -
minimises risk of your muscle action causing you to grip the lead. You can
still get a fatal shock this way if you are unlucky - YMMV.

.

RM

From: Sean H. Breheny <KILLspamshb7KILLspamspamCORNELL.EDU>
>Once again I must plead ignorance: Could someone please tell me what an RCD
>is?

1999\09\13@220135 by Sean H. Breheny

face picon face
Thanks for all the replies. Perhaps this is a good time to bring up a
question I posted a long while ago and never got a satisfactory answer: How
do most people get shocked in general? In other words, what is the usual
current path? Let's say that I grab a hot wire with one hand anf I am
touching a grounded case with my other hand. Well,then its obvious.

However, it seems to me that this would NOT occur in most cases. In most
cases, only the hot lead would be contacting the body. In that case, the
only available current path is into the floor. BUT, most floors are made of
non-conducting materials. SO, how is the circuit completed? OR, would
someone most likely not receive a shock in this case?

In addition, you often hear of lots of people getting killed by dropping an
electrical appliance into a bath tub. While I certainly recommend taking
all precautions to prevent this,I don't understand why it is so often
fatal. It seems to me that the obvious current path would be thru the
water,bypassing the person completely. Unless the person was holding the
appliance,in which case,again,the current path is obvious. However,this
probably wouldn't be the case if the appliance just "fell" into the
water,as the story often goes.

Sean

At 11:30 AM 9/14/99 +1200, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
spamBeGoneshb7spamBeGonespamcornell.edu ICQ #: 3329174

1999\09\14@055020 by Mark Willis

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"Most technicians are shocked as Management had the workbenches built of
metal, for extreme durability, and for "convenience" decided to ground
the entire bench with 12AWG wire - That way there's always a ground
handy when you need one."

(My high school's benches were this way, we tended to stay well clear of
HV stuff as if you were near the underside of the bench, your leg was
GUARANTEED to be grounded or at best *near* ground, if you were wearing
heavy long pants.  NOT recommended, IMHO, to build benches this way!)

I've seen techs working on live circuits, one habit for keeping you from
grabbing a falling charged object is to cram the unused hand into a rear
pants pocket, then make a fist, this tends to stop most people from
whipping that hand out in time to catch that falling HV wire or
whatever.

Worst current paths are across the center of the chest - from left arm
to right leg, etc.  From arm to arm doesn't hit the heart AS badly as
across the center of the chest, and of course neither's recommended <G>

 Mark

Sean H. Breheny wrote:
>
> Thanks for all the replies. Perhaps this is a good time to bring up a
> question I posted a long while ago and never got a satisfactory answer: How
> do most people get shocked in general? In other words, what is the usual
> current path? Let's say that I grab a hot wire with one hand anf I am
> touching a grounded case with my other hand. Well,then its obvious.
> <snipped>

1999\09\14@082020 by Fansler, David

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               Thanks for all the replies. Perhaps this is a good time to
bring up a
               question I posted a long while ago and never got a
satisfactory answer: How
               do most people get shocked in general? In other words, what
is the usual
               current path? Let's say that I grab a hot wire with one hand
and I am
               touching a grounded case with my other hand. Well, then its
obvious.

Back in 1955, Hurricane Hazel came through North Carolina.  The eye of Hazel
passed directly over the town I was living in.  During the fist part of the
storm, the neutral power line coming to our house came out of a screw
connector at the house - thus we lost 110vac.  There was about a 2 hour
period of calm while the eye passed, so my Father decided to fix the problem
his self.  He knew that holding the neutral wire was not a problem - as long
as he did not touch one of the hot wires.  Up on a ladder, he was finding it
hard to pull the neutral wire hard enough to get it into the connector.
Suddenly he found himself with the neutral in one hand and a hot wire in the
other.  He could not let go.  Fortunately, he had enough presence of mind to
kick the ladder out from under him.  The fall was enough to break his grip
on the wires.  He only suffered a broken foot (and probably some pride).  By
the time they returned from the hospital, the local power company had
restored our power, since he was injured.  I was only 4 at the time, and
Hazel probably is my earliest vivid memory.  My Father is 75 now and doing
well.

Here's hoping that Floyd (and Gert) miss NC - not that I willing wish
ill-will on SC or Georgia!

David V. Fansler  (Burlington, NC)
Network Administrator
AutoCyte, Inc.
336-222-9707 Ext. 261
TakeThisOuTdfanslerEraseMEspamspam_OUTautocyte.com <RemoveMEdfanslerspamTakeThisOuTautocyte.com>
Now Showing! http://www.mindspring.com/~dfansler
<http://www.mindspring.com/~dfansler>   Updated July 13, 1999


               Thanks for all the replies. Perhaps this is a good time to
bring up a
               question I posted a long while ago and never got a
satisfactory answer: How
               do most people get shocked in general? In other words, what
is the usual
               current path? Let's say that I grab a hot wire with one hand
anf I am
               touching a grounded case with my other hand. Well,then its
obvious.


1999\09\14@132012 by Mike Keitz

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On Tue, 14 Sep 1999 02:49:42 -0700 Mark Willis <mwillisEraseMEspam.....FOXINTERNET.NET>
writes:
> "Most technicians are shocked as Management had the workbenches built
> of
> metal, for extreme durability, and for "convenience" decided to
> ground
> the entire bench with 12AWG wire - That way there's always a ground
> handy when you need one."

Any metal object that is routinely touched needs to be grounded.
Otherwise it could become live and present a shock hazard by itself.  It
is bad practice to ground equipment to a bench.  If the bench ground is
defective, faulty equipment would make the bench live.  It is best though
to keep the number of conductive objects to a minimum where working with
live equipment.

>, this tends to stop most people from
> whipping that hand out in time to catch that falling HV wire or
> whatever.

Get in the habit to not reach for *anything* that falls off of a
workbench.  Your brain isn't fast enough to evaluate whether it is safe
to catch or not.  Instead watch yourself and jump back if needed so it
doesn't land on you.  You may see a few expensive objects fall to the
floor and break and wonder if you could have caught them.   But that's a
lot better than getting hurt by something that is too heavy, too hot,
electrified, caustic, etc. to handle.  The way to prevent things from
falling to the floor is to not let them get close to the edge in the
first place.


___________________________________________________________________
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1999\09\14@132802 by Andy Kunz

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>Get in the habit to not reach for *anything* that falls off of a
>workbench.  Your brain isn't fast enough to evaluate whether it is safe

I have a friend who instinctively caught an Xacto knife that was falling.

Stuck through his palm.  Fortunately it missed the ligaments.

Andy

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1999\09\14@150859 by M. Adam Davis

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Ouch.

Andy Kunz wrote:
> I have a friend who instinctively caught an Xacto knife that was > falling.
>
> Stuck through his palm.  Fortunately it missed the ligaments.

1999\09\15@135142 by paulb

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Sean H. Breheny wrote:

> Once again I must plead ignorance: Could someone please tell me what
> an RCD is?

 Residual Current Device(?).  Core Balance Relay - type circuit
breaker.

 Old Earth Leakage Circuit Breakers (ELCB) monitored current in the
earth line - no good if you contact the plumbing, so pretty useless and
rather unreliable when we had one, though it did trip when the 'fridge
defroster shorted out (it wouldn't reset - had to be turfed!).

 Core Balance Relay describes it all, both lines (Active and Neutral)
pass (once or more) through a toroidal transformer, a third winding on
which, with or without electronic amplification, operates the trip relay
within 50 ms.  Rated at 30 mA domestic, 10 mA medical.

 Common problem relates to using only one to "protect" a whole
household.  Fridges are commonly excepted as (well-grounded and cord
rarely open to damage) consequences in terms of food spoilage can be
very nasty.  *Proper* usage is one per power circuit.

 Most commonly tripped by (bugs in) dishwasher, other problem was with
moisture build-up in unused clothes-dryer heater.  I'm very surprised
the washing machine hasn't tripped it yet!
--
 Cheers,
       Paul B.

1999\09\15@154613 by Sean Breheny

face picon face
Hi Paul,

Thanks for the explanation. When you said that you were surprised that
the washing machine never tripped it,are you talking about the washer in
my house? If so, AFAIK, RCDs are NOT standard in US homes. In fact, I
have never seen such breakers (that I recognized,anyway) on a whole
circuit,only on individual low-current outlets (usually in bathrooms) and
integrated into certain appliances (usually hair dryers).

Do homes in OZ usually have one on each circuit?

Sean


On Tue, 14 Sep 1999, Paul B. Webster VK2BZC wrote:

{Quote hidden}

1999\09\15@164916 by paulb

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Sean Breheny wrote:

> When you said that you were surprised that the washing machine never
> tripped it,are you talking about the washer in my house?

 No, mine.

> Do homes in OZ usually have one on each circuit?

 Unsure on exact practice.  Rules say must have RCD on power circuits
in domestic use, not business(!).  As common practice is still to have
only two, maybe three power circuits per house, it would be sensible to
have two as previously mentioned.

 Of course I have as I may have mentioned, no less that seven power
circuits including two dedicated for computers and amateur radio,
initially fitted on three RCDs, but to be extended to at least five.

 (Problem: RCDs use two slots; so where 2 circuits were fitted with 1
RCD, had RCD and 2 current breakers, total 4 slots, replacement with
2 RCDs which include current break no problem.  3 circuits on one RCD
took 5 slots, can't be readily upgraded!)
--
 Cheers,
       Paul B.

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